In conventional vacuum cleaners (vacuums), dirt laden air is ducted into the vacuum and deposited into a receptacle supported on or within the vacuum housing. Although many previous vacuums have used a flexible bag as the dirt receptacle, the cost and inconvenience of replacing such bags has led to an increased preference for bagless vacuums. Bagless vacuums separate dirt by cyclonic action and/or duct the stream of dirt-laden air through a reusable filter that filters the dirt particles from the air stream before exhausting the filtered air stream back into the atmosphere. Various different types of filter have been used in bagless vacuums, such as HEPA (High Efficiency Particulate Air) filters and rigid porous plastic materials. In many bagless vacuums, the dirt and dust are stopped by the filter and fall into a removable receptacle for later disposal, but in some cases the filter itself may be shaped to form the dirt receptacle or a portion of the dirt receptacle, much as vacuum bags do. When the bagless vacuum's filter becomes clogged, it can be cleaned by shaking dirt and dust out if it or by using water or detergent to flush the dirt out.
Although bagless vacuums often provide suitable initial vacuuming performance, their filters tend to become clogged during use as debris accumulates on the filter surface, which results in a reduction in the pressure drop (and thus the vacuuming power) at the surface being vacuumed. Although cleaning the filter between uses prolongs the filter life, over time, debris becomes permanently embedded in the filter, despite efforts to clean them. Such clogging leads to reduced vacuuming power, and reduced user satisfaction. As such, it eventually becomes necessary to replace the filter to return the vacuum to suitable performance. In many cases, replacement filters can be relatively costly, or may no longer be available. Furthermore, bagless vacuum filters can sometimes be rapidly clogged by large volumes of large particles that impinge upon and block the filter, and require the user to immediately stop vacuuming to remove the particles from the filter.
Various cyclonic separators have been introduced to help reduce reliance on filters in bagless vacuums. Such cyclonic devices typically introduce the air into a collection chamber in a tangential manner or otherwise induce a cyclonic rotation to the air, and remove the air through an outlet duct located in the axial center of the chamber. Examples of typical cyclonic vacuums are shown in U.S. Pat. Nos. 5,267,371, 6,532,621, 6,536,072, 6,578,230, 6,599,340, 6,625,845, and 6,757,933, all of which are incorporated herein by reference. While such cyclonic vacuums are useful, it has proved difficult to provide a consumer-level vacuum that efficiently and consistently separates particles, dust and other debris from the working air flow without using filters or vacuum bags to physically block the passage of the debris, or resorting to a highly complex and often expensive arrangement of cyclone separators. It has also been difficult to provide a vacuum that efficiently and consistently separates larger particles from dust and other small particles to inhibit the impingement of large particles on the vacuum filter. It has further been difficult to provide a cyclonic separation system for vacuum cleaners that is compact and relatively flexible in the manner in which it can be incorporated into the vacuum cleaner.